There is an organism living on this planet who can travel through space without a suit. Cute, unassuming little invertebrates, these organisms are called tardigrades, or water bears, and usually spend their days crawling around on a piece of nice wet moss in a forest, or meandering through our vast oceans. They only grow to be about 1.5 millimeters long, but over 1,000 species of them inhabit the planet, and they all have a superpower unmatched by any other species on Earth. No now knows why, but tardigrades can withstand temperatures as cold as liquid nitrogen, radiation doses that would kill a human 100 times over, thrive in an outer-space-like vacuum, and survive without water for years.

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Tardigrades have perfected an extreme form of hibernation called an anhydrobiotic state, meaning roughly that they can expel all of the water from their cells and go into a state of suspended animation. They usually only live for about a month when left in an active state, but once they dry themselves out, they can survive the harshest conditions the world can throw at them for decades on end.

Evolving to live through cold and drought makes sense — these types of conditions occur all the time on Earth. But extreme radiation? Vacuum? Some scientists believe these traits are just a byproduct of their hibernation, but in truth it remains a mystery.

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Are tardigrades aliens from a distant world who came to Earth on an asteroid? Probably not — they're genetically related to the well known worm c. elegans. But last fall, the European Space Agency sent the little guys into orbit as part of the BioPan-6 mission to see how well they'd do floating above their homeworld, exposed to outer space. We're still waiting on the results of those experiments, which hopefully will shed light on why these mysterious little creatures evolved to become the toughest life on the planet.